Thanks all. I'm not a newbie at any of this so I should probably do a search when I think of one of these idiosyncratic topics before starting a new, potentially repetitive thread. But sometimes I just jump the gun

Anyhow, I'm going to run the simple test from the end of that chapter, but agree with Mark Walker that even if anyone has this problem there doesn't seem to be much you can reasonably do about it.

Sometime ago (before I had Cteins book) I read that prints on VC paper might be not really sharp because of the sensitivity to UV. I made a simple test: raise the head as far as possible (resulting in a mag. of 17), make a print with and without UV filter. Guess what - no difference visible (EL Nikkor N 50/2.8), case closed.

I think the OP brings up a valuable point. I have just re-read Ctein's book again and confess:

1. I didn't fully understand the section but was astounded by the figure of 15mm, thinking as Michael did that this would show up as plain as your nose
2. I still cannot figure out why this kind of problem didn't spread worldwide alarm at the time of his publication and protests to paper manufacturers. You'd think that it would have entered into the annals of darkroom disasters and still be talked about

3. Is it possible that whatever was causing the problem that Ctein saw could somehow have been peculiar to his set-up, unlikely as this seems? Might paper manufacturers have since done something to rectify the issue?

Ath had no issue and neither or so it would seem, did the majority of users so what was happening in Ctein's tests?

Unfortunately he does not go on to say why it may be that most users will never experience the issue and yet the very fact he devotes a section of his book to it indicates that he thought it a serious enough issue to put it before his readers.

Actually there are a number of "alarms" raised by Ctein in the book which does not seem to have engaged the darkroom world such as serious issues with, I think, some makes of RC paper which he cites and which should be a separate thread. Again maybe the issues he and a fellow photographer of high standing experienced were not that widespread and have been subsequently solved.

I haven't got the date of the book but it would appear that he was speaking of issue in the mid 1990s

If you have ever tilted an easel to try to correct converging parallels, most likely you have needed at least that amount of depth of focus.

Matt

“Photography is a complex and fluid medium, and its many factors are not applied in simple sequence. Rather, the process may be likened to the art of the juggler in keeping many balls in the air at one time!”

Ansel Adams, from the introduction to The Negative - The New Ansel Adams Photography Series / Book 2

Ctein is a very clever fellow and anyone who reads his books and articles will know how scientific his analysis is. He is essentially looking at the fine margins of printing which, as with all worthwhile study in detail, has a broader implication and comes with useful insight: delving into the real nitty-gritty of what occurs in a process, for example. Ultimately, it is what creates further development and he had responses from paper and lens manufacturers on this issue (and they concurred that there is a focus factor), which is no mean feat. Furthermore, the possible solution creates another set of theoretical problems: as with most things compromise is the result, but at no great cost to ourselves, quite the reverse.
Personally, I can live with the fact that I am not going to achieve 'perfect' pictures, but I am grateful that others are looking into this and giving me the benefit and, maybe, helping to keep alive the advancement of our silver world. (It's what the good forums, like this one, thrive on and perpetuate).
Thanks, Mark Walker.

Seems to me you vould tell in one print if you have a problem. Tilt the paper 2 inches high at on end and focus in the middle. (If you had a picture of a ruler wouldn't that be great.) See wher your focus lies aftr you process the print.
Let us know

"There are a great many things I am in doubt about at the moment, and I should consider myself favoured if you would kindly enlighten me. Signed, Doubtful, off to Canada." (BJP 1914).

Sometime ago (before I had Cteins book) I read that prints on VC paper might be not really sharp because of the sensitivity to UV. I made a simple test: raise the head as far as possible (resulting in a mag. of 17), make a print with and without UV filter. Guess what - no difference visible (EL Nikkor N 50/2.8), case closed.

That's because tungsten lamps (including halogen) emit virtually no energy in the UV portion of the spectrum.

If you used direct unfiltered sunlight as the light source for your enlarger, you might notice a difference.

Perhaps such experienced forum readers (and writers) can go beyond simple expressions of dismay and provide links to the relevant threads which in the past have resolved this issue (these issues), at least to the extent they can be resolved in this Enlarging forum. Failing that, at least they could point out the relevant thread titles or keywords for searches (though if they can do that then they can probably provide links to the best threads).